Hammer suspension for high speed printer



June 1955 L. w. MARSH, JR 3,137,668

HAMMER SUSPENSION FOR HIGH SPEED PRINTER Filed June 27, 1963 FIG. I

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FIG. 6 I4 28%!49 1m J FIG. 7 INVENTOR.

LYNN W. MARSH, JR.

ATTORNEYS United States Patent 3,187,668 HAMMER SUSPENSIGN FDR HIaGHSPEED PREITER Lynn W. Marsh, In, Marblehead, Mass assignor to ANelexCorporation, Boston, Mass., a corporation of New Hampshire Filed .l'une27, 1963, Ser. No. 291,012 4 Claims. (Cl. 101-93) This invention relatesto an improved hammer suspension for high speed printers of a typegenerally disclosed and claimed in U. S. Patent No. 2,940,385 to FrankR. House, entitled High Speed Printer, issued June 14, 1960, andassigned to the assignee of the present application.

The above patent describes a high speed printer of a type having arotatable print wheel with a series of characters circumferentiallyspaced thereabout, together with a series of hammers mounted in radialjuxtaposition to the periphery of the wheel for actuation by electricalimpulses to imprint a desired series of characters on paper passingintermediate the print wheel and hammer. According to the patent, thehammers are pivotally mounted by means of individual reed springs, so asto be actuable by solenoid devices. However, it has been found inpractice that the hammers tend to oscillate after actuation, and maystrike the paper against the print wheel more than once as the hammeroscillates. This may smear the paper, or produce a second ghostimpression on the rebound. For this reason, external damping may benecessary, and takes the form of return springs, according to theaforementioned patent. However, these return springs are slidablyengaged withthe hammer, and introduce friction into the suspension. Theyquickly Wear the hammer because of the high frequency of actuation towhich it is subjected. Furthermore, this type of suspension is subjectto fatigue after a period of use.

It is the principal object of the present invention to provide animproved hammer suspension for a high speed printer, which isfrictionless and therefore free of wear from this cause. The improvedsuspension features internal spring return and damping action. It is afurther object of the invention to provide an improved hammer suspensionwhich is less subject to fatigue. Another object is to provide internaldamping of hammer oscillation, to prevent rebounding impact with theprint wheel following release of the hammer. It is a further object ofthe invention to provide a hammer suspension with pro-stressing meansfor causing the suspension to oscillate about a position other than itsneutral position, thereby to prevent rebound into a print wheel. Furtherobjects and advantages of the invention will become apparent as thefollowing description proceeds.

Briefly stated, according to a preferred embodiment thereof, 1 may carryout my invention by supporting a hammer block in the free end of a firstflexible beam whose opposite end is fixed in a stationary block,mounting an actuating block in the free end ofa second flexible beamwhose opposite end is fixed in the stationary block, and fixing theopposite ends of still a third flexible beam in the hammer block andactuating block, to form in eifect a parallel spring linkage supportingthe hammer and actuating blocks from the stationary block. The first andsecond beams are substantially coaxial, and both are parallel to thethird beam. The dimensions and flexural characteristics of the threebeams are selected to give a desired spring rate to the entiresuspension system, and desired damping characteristics. The naturalfrequencies of the three beams being unequal, the system affords naturaldamping of oscillation. Upon the application of a deflecting force tothe actuating block, the beams flex according to the compositecharacteristic of the linkage to deflect the hammer block in an oppositesense, into abutment with the print wheel. Upon release of the actuatingblock, the return of the hammer to the neutral position is governed bythe composite damping characteristics of the beams.

The system may be pre-stressed so that oscillation of the hammer takesplace about the pre-stressed position rather than about a neutralposition, and rebounding of the hammer into the print wheel may beprevented in this fashion; In a preferred form, either the beams hasadjustable connection with one of the hammer or actuating block, so thatits effective length may be adjusted to pre-stress that particular beamin tension or compression. The system will then oscillate about thepre-stressed position, rather than about the neutral position, of thespring lever system. Preferably, the beams are tubular in form to permit.pre-stressing with a minimum of fatigue. The pre-stressing adjustmentcan also be utilized to insure that the face of the hammer is squarewith the print wheel characters at the point of impact. If additionaldamping is required, a further beam may be cantilevered in one or theother of the hammer and actuating blocks, and received in a stationaryexternal slide so as to dampen the oscillation of the suspension linkagewithout interfering with its flexure.

While the specification concludes with claims particularly pointing outthe subject matter which I regard as my invention, it i believed that aclearer understanding may be gained from the following detaileddescription of preferred embodiments thereof, referring to theaccompanying drawings, in which:

FIG. 1 is a view in elevation showing a preferred form of the improvedsuspension in an undeflected condition;

FIG. 2 is a sectional view taken along line 22 in FIG. 1, looking in thedirection of the arrows;

FIG. 3 is a schematic view in elevation showing the suspension of FIG. 1in a pre-stressed condition;

FIG. 4 i a view similar to FIG. 3, but showing the suspension deflectedin a manner to actuate the hammer; and

FIGS. 5-7 are schematic views in elevation showing various modificationsin which external damping is applied to the suspension system.

Referring to FIGS. 1-2, a preferred construction is shown in operativerelation to a rotatable print wheel 2 having spaced about its peripherya serie of raised characters 3. The suspension serves to support ahammer block 4 in radially spacedrelation to the print wheel, so thatthe hammer block may be driven against the characters 3 to print themupon a moving sheet of paper 5 by means of a carbon sheet 6, all asgenerally described in the aforementioned House Patent No. 2,940,385.

In the preferred form, the suspension is supported in a stationary block7 mounted upon a base member 8, and includes a first flexible beam 11and a second flexible beam 12 which are substantially coaxial andcantilevered in the block 7, and aflixed at their free ends to thehammer block 4 and to an L-shaped actuating block 14, respectively. Thehammer block 4 and actuating block 14 are further interconnected by athird flexible beam 15, substantially parallel to both the first andsecond beams, to form a parallel spring linkage. According to a featureof the invention, the effective length of the beam 15 may be adjusted topro-stress the suspension, by means of a knurled nut 17 threaded on areduced end portion 18 of the beam 15, which is slidably receivedthrough the hammer block 4 for this purpose. By these means, thesuspension may be variably pre-stressed, as is illustrated in FIG. 3.

In the preferred form, the beams 11, 12 and 15 are tubular in form, topermit pre-stressing with a minimum of fatigue. While the dimensions andspring constants of the various beams may be selected to give desireddeflection and damping characteristics, the beam 15 is relatively stiffin the form shown, While the beam 11 is designed to be somewhat moreflexible than the beam 12. The differing natural frequencies ofvibration of the various beams provide internal damping action. Toactuate the hammer into impact with the print wheel, a solenoid isprovided, comprising a coil 29 and a core structure 22, which is offerromagnetic material, as is the block 14. Application of current tothe coil applies a downward force to the block 14 as shown at F in FIG.4, which deflects the suspension as shown by that figure, driving thehammer block upwardly into contact with the print Wheel. Subsequentrelease of the actuating force permits the beams to return the hammer toits initial position by a spring action, with an oscillation-dampingcharacteristic which depends upon the individual characteristicsof thebeams 11, 12 and 15. With the suspension pre-stressed as shown in FIG.3, the suspension will oscillate about this position, rather than aboutthe neutral position of FIG. 1, with the result that the hammer blockmay be prevented from striking the print wheel on rebound, and therebyavoid forming ghost impressions, and smearing of the paper by thecarbon.

Referring to FIGURES 5,. 6 and 7, modified forms are shown in whichadditional damping and spring action is alforded by aflixing anadditional flexible beam 24 in either of the blocks 4 or 14, extendingcoaxially with either the beam 15 or the beams 11 and 12. The free endof the beam 24 is slidably received by a slideway 26 in astationarysupport member 28, so that the beam 24 accepts torsionalmoments applied by flexure of the suspension, but is longitudinally freeso as not to interfere with the desired flexural movement. It will beapparent that by proper selection of the dimensions and spring constantsof the various beams, desired composite damping and flexingcharacteristics may be secured.

While preferred embodiments of the improved hammer suspension have beendescribed by way of illustration, it

will be apparent to those skilled in the art that various changes andmodifications may be made Without departing from the true spirit andscope of the invention, which I therefore intend to define in theappended claims without limitation to the details of the foregoingembodiments.

What I claim is;

1. In a high speed printer, a print wheel and a hammer block constructedand arranged for impacting said print wheel, a flexible suspension forsaid hammer block comprising a stationary base member, a freely movableactuating block, a first flexible beam cantilevered at one end thereofin said base member, extending in one direction therefrom, and atfixedat an opposite end thereof in said hammer block, a second flexible beamsubstantially c0- axial with said first beam and cantilevered at one endthereof in said base member, said second, beam extending in anopposite'direction than said first beam from said base member, andaflixed at an opposite end thereof in said actuating block, and a thirdflexible beam affixed at opposite ends thereof in said hammer blockandsaid actuating block, said first and second beams extending generallyparallel to said'third beam to form a deflectable suspension flexiblysupporting said hammer block and said actuating block on said basemember, means for releasably moving said actuating block in a directiontransverse to the parallel extent of said beams, for effectingoscillatory displacement of said hammer block into engagement with saidprint wheel upon movement and subsequent release of said actuatingblock.

2. The combination recited in claim 1, in which at least one of saidbeams is adjustably affixed in one of said blocks for adjustment of theeffective length of said one beam, whereby said suspension may bepre-stressed to a flexed position about which said suspension oscillateswhen deflected and subsequently released.

3. The combination recited in claim 1, together with at least onefurther flexible beam cantilevered at one end thereof in one of saidblocks, said further beam being slidably received in said stationarybase member for restraint against bending moments applied by flexure ofsaid suspension. V

4. The combination recited in claim 1, in which said beams havedifferent flexural characteristics to afford internal damping ofvibration of the suspension.

References Cited by the Examiner UNITED STATES PATENTS 3,041,964 7/62Simpsonet al. 3,072,045 1/63 Goin.

WILLIAM B. PENN, Primary Examiner.

1. IN A HIGH SPEED PRINTER, A PRINT WHEEL AND A HAMMER BLOCK CONSTRUCTEDAND ARRANGED FOR IMPACTING SAID PRINT WHEEL, A FLEXIBLE SUSPENSION FORSAID HAMMER BLOCK COMPRISING A STATIONARY BASE MEMBER, A FREELY MOVABLEACTUATING BLOCK, A FIRST FLEXIBLE BEAM CANTILEVERED AT ONE END THEREOFIN SAID BASE MEMBER, EXTENDING IN ONE DIRECTION THEREFROM, AND AFFIXEDAT AN OPPOSITE END THEREOF IN SAID HAMMER BLOCK, A SECOND FLEXIBLE BEAMSUBSTANTIALLY COAXIAL WITH SAID FIRST BEAM AND CANTILEVERED AT ONE ENDTHEREOF IN SAID BASE MEMBER, SAID SECOND BEAM EXTENDING IN AN OPPOSITEDIRECTION THAN SAID FIRST BEAM FROM SAID BASE MEMBER, AND AFFIXED AT ANOPPOSITE END THEREOF IN SAID ACTUATING BLOCK, AND A THIRD FLEXIBLE BEAMAFFIXED AT OPPOSITE ENDS THEREOF IN SAID HAMMER BLOCK AND SAID ACTUATINGBLOCK, SAID FIRST AND SECOND BEAMS EXTENDING